1. Field of the Invention
The present invention relates to a method for controlling operations of a backlight unit of a liquid crystal display, and more particularly, to a method of reducing blurring of moving images by controlling the operations of the backlight unit.
2. Description of the Prior Art
A liquid crystal display (LCD) has advantages of being light weight, having a low power consumption, giving off low radiation and the ability to be applied to various portable electronic products such as notebook computers and personal digital assistants (PDAs). In addition, LCD monitors and LCD televisions are gaining popularity as a substitute for traditional cathode ray tube (CRT) monitors and televisions. However, due to their physical limitations, the liquid crystal molecules need to be constantly rotated and rearranged while image data is changed, which often causes a delay phenomenon. Consequently, the delay phenomenon becomes even worse when a liquid crystal display is showing moving pictures.
In order to resolve the common blurring phenomenon while the LCD is showing moving pictures, the related art often utilizes a method by inserting a black frame or shutting down the backlight unit at particular block of the display. Please refer to FIG. 1. FIG. 1 is a timing diagram showing the means of controlling a liquid crystal display 10 by inserting a black frame according to the prior art. As shown in FIG. 1, the liquid crystal display 10 includes a liquid crystal display panel 12 and a backlight unit 14. Ideally, the liquid crystal display panel 12 functions to control the rotation of the liquid crystal molecules for changing the transmittance of each pixel and producing the desired image corresponding to the image signal received. The backlight unit 14, on the other hand, includes a plurality of illumination devices 16 to generate light to illuminate the liquid crystal display panel 12 and enhance the brightness of the image produced by the liquid crystal display panel 12. In order to prevent the liquid crystal display 10 from producing the blurring phenomenon while displaying moving images, the conventional solution often involves inserting a black frame for every two frame periods. FIG. 1 shows the display status of the liquid crystal display 12 within four consecutive frame periods, in which each of the time intervals t2−t1, t3−t2, and t4−t3 includes a frame period, and the liquid crystal display 12 between time t1 and t3 includes a black frame.
Please refer to FIG. 2. FIG. 2 is a timing diagram showing the means of controlling the liquid crystal display 20 by turning off the backlight unit 24 periodically. In contrast to the insertion of a black frame from FIG. 1, the liquid crystal display 20 turns off the backlight unit 24 within two frame periods corresponding to time t1 and t3 thereby preventing the plurality of illumination devices 26 from illuminating during these two frame periods. Hence, the visual effect of the liquid crystal display 20 is essentially identical to the liquid crystal display 10 utilizing the black frame insertion method.
Additionally, N. Fisekovic et al. discloses an article “Improved Motion-Picture Quality of AM-LCDs Using Scanning Backlight” from the book “Asia Display/IDW '01”. Please refer to FIG. 3. FIG. 3 is a status diagram showing another means of reducing the blurring phenomenon of moving images according to the prior art. As shown in FIG. 3, a liquid crystal display 30 includes a liquid crystal display panel 32 and a backlight unit 34, in which the backlight unit 34 further includes a plurality of illumination devices 36 to generate light and illuminate the liquid crystal display panel 32. Preferably, the liquid crystal display 30 reduces the visual blurring phenomenon by turning only one of the illumination devices 36 on within the same period. Please refer to FIG. 4 and FIG. 5. Disclosed in Fisekovic et al's article, FIG. 4 is a perspective diagram showing a liquid crystal display 40 and FIG. 5 is a timing diagram of the initiating time of each illumination device 46A to 46D and the corresponding gray scale of each pixel of the liquid crystal display 40 from FIG. 4. As shown in FIG. 4, the liquid crystal display 40 also includes a liquid crystal display panel 42 and a backlight unit 44, in which the backlight unit 44 includes a plurality of illumination devices 46A to 46D to generate light and illuminate the liquid crystal display panel 42. Similar to the backlight unit 34 of the liquid crystal display 30, only one of the illumination devices 46A to 46D of the backlight unit 44 will be turned on within the same period. FIG. 5 also illustrates four gray scale curves I, II, III, and IV of the pixels illuminated by the illumination devices 46A to 46D, in which each gray scale curve I to IV indicates a gray scale transformation of the corresponding pixel. For instance, curve I indicates the gray scale transformation of the pixels illuminated by the illumination device 46A within a time period T, and when the gray scale of the pixel undergoes a transformation, a delay phenomenon will result as the arrangement of the liquid crystal molecules will not be able to react in time. In order to prevent the gray scale transformation of the pixels before stabilization from being observed, each of the illumination devices 46A to 46D will be turned on after the liquid crystal direction of each of its corresponding pixels is stabilized. As shown in FIG. 5, each shadow represents the timing where each illumination device 46A to 46D is turned on, during which all of the gray scale of the corresponding pixels are transformed and stabilized. Nevertheless, the method ultimately brings out a disadvantage that since only one of the illumination device is turned on within the same period, the brightness of the liquid crystal display 40 will become insufficient and a larger electrical current will have to be applied on the illumination devices 46A to 46D to increase the brightness. However, increasing the electrical current also increases the necessity of making numerous measurements for performing safety precautions, providing a source of large electrical current for providing enough brightness, and providing a modified circuitry design for enhancing the fabrication process.